The present invention is directed to mechanisms for adjusting the position of the rear axles on a dual axle truck semi-trailer. In particular, the present invention is directed to a mechanism which permits the rapid and easy reallocation of weight on such a semi-trailer.
Presently, there are over 1.1 million tractor trailers in operation in the United States. Tractor-trailers are subject to extensive Federal and state weight regulations. The violation of these weight regulations may result in fines and penalties to the operator or owner of the trailer. When a tractor-trailer combination is loaded very near to its legal limit, it will frequently be weighed at a roadside weigh-station. Under applicable regulations, the weight of the loaded trailer must be distributed under a calculation known as the xe2x80x9cbridge formulaxe2x80x9d. The bridge formula determines the distribution of weight within the trailer and factors in the distance between the cab and the rear axles of the semi-trailer. When a truck is stopped on the road for a random weight measurement, it may have too much weight distributed over the rear axles. If the weight distribution falls outside the acceptable limits under the bridge formula, the truck will not be permitted to continue until the weight has been properly redistributed.
Rather than redistribute the weight within the trailer itself (which, depending on the cargo carried may be an impossible task), the operator customarily redistributes the weight by moving one or both of the axles of the semi-trailer. Unfortunately, the movement of the axles when a trailer is fully loaded is a difficult task. Most semi-trailers incorporate a wheeled tandem affixed to a carriage which is slidably adjustable along an apertured track on the trailer and which is retained in position by locking devices inserted into the apertures.
Presently, the vast majority of trailers are readjusted in the following manner: The operator (1) locks the rear tandem into place using the tandem axles brakes, (2) pulls a lever to disengage the locking pins, thus freeing the carriage to be adjusted along the trailer""s length, (3) drives the tractor and trailer forward or back to drag the trailer overthe locked tandem axles till they are in the new desired position, and (4) releases the lever pulled in step 2 so that the pins re-engage in the new desired set of apertures, again locking the carriage position relative to the trailer.
There are several problems associated with this method for readjusting the position of a rear tandem. Initially, this method relies largely upon trial and error before the correct positioning is achieved. Because this method relies upon the power of the vehicle tractor to slide the trailer, precise incremental movements of the trailer are usually not possible. Furthermore, it is frequently difficult to manually remove the locking pins from the apertures. This may be particularly problematic in cold or inclement weather, or when the pins are frozen, locked or rusted.
Various alternative methods have been devised to redistribute the weight of a semi-trailer. U.S. Pat. No. 3,203,711, for example, discloses a floating axle attachment in which a fifth floating axle is slid beneath the semi-trailer. This method is expensive and requires a specialized cab and trailer configuration. Another type of prior art device adjusts the location of the trailer coupling in order to effectuate weight distribution and transfer. See, U.S. Pat. Nos. 2,832,610; 4,662,670; 3,402,944 and 2,153,468. The devices disclosed in these patents are similarly complex and require expensive hydraulic cab configurations. U.S. Pat. No. 2,153,468 discloses a load redistribution system which incorporates a separate trailer dolly which rides on the main trailer bed. A third type of prior art device is directed to a system which adjusts the length of the chassis or trailer bed. See U.S. Pat. No. 2,371,261. This method is similarly expensive and requires specialized trailer configurations.
One quite effective mechanism of the prior art for solving the tandem adjustment problem is that of U.S. Pat. No. 5,346,233, which discloses a power-actuated device which is simple and safe to operate in adjusting the position of the rear tandem.
After the invention of the adjustment system of U.S. Pat. No. 5,346,233, there has still been a need to further simplify and standardize the mechanism by which various mechnical and hydraulic actuators may be attached to the trailer and tandem of the truck. In particular, there has been a need to reduce the number and type of parts comprising the system. In addition, there has been a need to reduce the number of hydraulic cylinders employed from two to one, thus eliminating expense, alignment issues, and maintenance load. Along with the other needs recognized by the inventor of U.S. Pat. No. 5,346,233, the present invention represents a simplification of manufacture, installation, operation, and maintenance for a slide system for adjustment of the position of the tandem relative to the trailer.